OOP dalam python

class Hero:

    def __init__(self,name,health,attackPower,armor):
        self.name = name
        self.health = health
        self.attackPower = attackPower
        self.armor = armor

    def serang(self,lawan):
        print(self.name + ' menyerang ' + lawan.name)
        lawan.diserang(self,self.attackPower) -> funtion ini?

    def diserang(self,lawan,attackPower_lawan):
        print(self.name + ' diserang ' + lawan.name)
        attack_diterima = attackPower_lawan / self.armor
        print('serangan terasa ' + str(attack_diterima))
        self.health -= attack_diterima
        print('darah ' + self.name + ' tersisa ' + str(self.health))

kenapa fungsi dengan nama (diserang) berhasil dipanggil didalam fungsi (serang)?

padahal fungsi diserang baru dideklarasikan setelah fungsi (serang)

tolong dijelaskan ya...